A power supply unit (PSU) performs processing, such as rectification, voltage reduction, etc., on an input voltage, and supplies a stable power supply voltage suitable for various kinds of units, such as a hard disk drive (HDD), etc., in an apparatus to which the PSU pertains. The PSU handles a high voltage current, and thus if a failure occurs in the PSU, heat might be generated, or an abnormality might occur in the power supply voltage which is supplied to each of the units in the apparatus. This might result in failures of the individual units. In order to avoid these problems, a PSU has a function of independently monitoring its own state all the time, and performing degeneration processing by itself immediately if the PSU has detected a failure. Stated differently, in a conventional system the PSUs are not collectively monitored. Rather each PSU only monitors itself.
In this manner, typical functions of the PSU include a function of converting an input voltage into a stable power supply voltage suitable for each unit in the apparatus, a function of monitoring a state of the PSU itself and performing degeneration processing by itself immediately at failure detection time, and a function of detecting occurrence of a power failure and informing a unit in the apparatus of the power failure.
In a RAID (Redundant Array of Independent Disks) apparatus, which is an example of a large-scale storage apparatus, a plurality of controller units and a plurality of HDD units are connected through a network in order to maintain expandability and redundancy, and to perform communication among the individual units so that a coordinated operation as one unit of a storage apparatus is performed.
FIG. 1 illustrates an example of a configuration of a RAID apparatus. In the RAID apparatus 1 illustrated in FIG. 1, HDD units 3-1 to 3-N (N is a natural number of two or more) are connected through networks 4-1 and 4-2, respectively. Each HDD unit 3-i (i=1 to N) has two PSUs 3i1 and 3i2, and a plurality of HDDs 3i3. For example, the HDD unit 3-1 has two PSUs 311 and 312, and a plurality of HDDs 313.
One of the PSUs 311 to 3N1 of the individual HDD units 3-1 to 3-N convert an input voltage obtained from a first power supply system 21 through a power cable 5-1 to a suitable power supply voltage, and supply the voltage to individual sections in the HDD units 3-1 to 3-N. Also, the other of the PSUs 312 to 3N2 of individual HDD units 3-1 to 3-N convert an input voltage obtained from a second power supply system 22 through a power cable 5-2 to a suitable power supply voltage, and supply the voltage to the individual sections in the HDD units 3-1 to 3-N.
In this manner, in the individual HDD units 3-1 to 3-N, the PSUs are duplicated (or made redundant), and thus even if one of the PSUs fails, it is possible to supply a power voltage from the other of the PSUs. Accordingly, even if one the PSUs fails, and degeneration processing is performed by the failed PSI, it is possible to continue operation by the RAID apparatus 1 as a whole. For example, if a power failure occurs in the first power supply system 21 in FIG. 1, it becomes impossible for one of the PSUs 311 to 3N1 to supply a power voltage. However, if the power supply system 22 is normal, the other of the PSUs 312 to 3N2 may supply a power voltage to individual sections in the HDD units 3-1 to 3-N, and thus it becomes possible to perform normal operation as the RAID apparatus 1.
The individual PSUs monitor an input voltage, and detect a power failure. However, for a special power failure in which an input voltage temporarily becomes unstable, there are cases where a power failure is not detected. Also, the PSU may not be able to perform voltage conversion normally because of an unstable input voltage. In this case, the PSU may determine that a failure has occurred within the PSU itself, and perform degeneration processing.
FIG. 2 is a diagram illustrating an example change in an input voltage resulting from a normal power failure at a normal power failure time. FIG. 3 is a diagram illustrating an example change in an input voltage resulting from a special power failure at a special power failure time. In FIGS. 2 and 3, the vertical axis shows input voltage from the power supply system to the PSU in any units, and the horizontal axis shows time in any units.
As shown in FIG. 2, it is possible for the PSU to detect a normal power failure in which an input voltage suddenly drops to a certain potential. That is to say, if the input voltage drops to a certain potential within a certain time period, the PSU detects a power failure, for example.
However, for example, as shown in FIG. 3, if an input voltage becomes unstable for a certain period of time, and it takes a longer time than a certain period of time for the input voltage to drop to a certain potential, the PSU may not be able to perform normal voltage conversion because of the unstable input voltage. If the PSU cannot perform normal voltage conversion of the input voltage, the PSU may detect its own failure. However, in reality, the reason inhibiting or preventing the performance of the normal voltage conversion is a special power failure, and the PSU itself has not failed in the case of FIG. 3, for example. However, using conventional techniques, the PSU may determines that the PSU itself has failed, and the PSU may perform degeneration processing. Accordingly, until the PSU that has performed degeneration processing by itself is repaired or replaced, it is not possible to use the RAID apparatus 1 in a state of redundant PSUs.